1. Field of the Invention
Our invention is a square hole drill which operates by virtue of its cutting head configuration and combined drive train.
2. Description of the Prior Art
Square hole drills using a cutting head based on the Reuleaux triangle configuration are known. A good explanation of the properties of the Reuleaux triangle can be found in the Scientific American magazine of February, 1963 beginning on page 148 in the article entitled "Curves of constant width, one of which makes it possible to drill square holes" by Martin Gardner. In the patent literature the best known references are the United States Patents to S. R. Powell and H. J. Watts bearing U.S. Pat. Nos. 2,586,084 and 1,241,176, respectively. In each of these references the rotation of the Reuleaux triangle cutting head is accomplished by a pure rotary drive with a square guide for the head and a floating chuck for its drive shaft.
The prior art square hole drills have definite drawbacks and limitations in their use. Most of these can be traced to the lack of a positive stable drive train for the cutting head. When a square hole guide tube or other restraining type of device has to be used with the cutting head to insure its proper movement, it creates an additional piece of equipment near the cutting surface which can limit the extent of use, especially for large and deep drilling operations as in the mining field. What we have done is to invent a positive planetary gear drive specifically made for the Reuleaux triangle type of cutting head thus eliminating external guides for the head and floating chucks for its drive. In this way our square hole drill is not only free standing, operative to cut large and/or deep holes, but can be designed to operate in practically any substance. Different sized cutting heads can, within about a fifty percent size range, be adapted to fit on the same drive train. Should the hole size to be drilled fall outside of this range, changes can be made to the gear train to accommodate the new sized cutting heads.